The invention relates to a method and apparatus for isolating a formation when completion equipment is removed from a well.
A completion string may be positioned in a well to produce fluids from one or more formation zones. Completion devices may include casing, tubing, packers, valves, pumps, sand control equipment, and so forth to control the production of hydrocarbons. During production, fluid flows from a reservoir in the formation through the perforations and casing openings into the wellbore and up a production tubing to the surface. The reservoir may be at a sufficiently high pressure such that natural flow may occur despite the presence of opposing pressure from the fluid column present in the production tubing. However, over the life of a reservoir, pressure declines may be experienced as the reservoir becomes depleted. When the pressure of the reservoir is insufficient for natural flow, artificial lift systems may be used to enhance production. Various artificial lift mechanisms may include pumps, gas lift mechanisms, and other mechanisms. One type of pump is the electrical submersible pump (ESP).
If a failure occurs in one or more completion components located downhole, then a portion of the completion string may need to be removed from the wellbore for repair at the surface. Such repair may take an extended amount of time, e.g., days or weeks. After repair is completed, the completion string portion may be lowered back into the wellbore and re-positioned to again start well production.
When an upper section of the completion string (e.g., production tubing, packers, pumps, etc.) is removed from the wellbore, some action may be taken to ensure that formation fluid does not continue to flow to the surface. This is typically done, for example, by applying some type of heavy weight fluid (also referred to as xe2x80x9ckill fluidxe2x80x9d) into the wellbore to xe2x80x9ckillxe2x80x9d the well, that is, to prevent fluid flow from the formation to the surface during work-over operations. Another technique to kill a well includes application of xe2x80x9cfluid loss control pills,xe2x80x9d which involves application of a heavy weight chemical to plug perforations in the formation. However, such techniques to kill a well may damage a formation and result in loss of production. Thus, a need exists to protect a formation from damage when a section of a completion string is removed from a well.
In general, according to one embodiment, an apparatus for use in a wellbore that passes through a formation includes a flow conduit capable of receiving a fluid flow from the formation and an isolation system coupled to the flow conduit and including one or more uni-directional flow control devices. The one or more uni-directional flow control devices are adapted to be opened by fluid flow from the formation and to be closed by pressure from a fluid column in the flow conduit when the fluid flow is shut off.
In general, according to another embodiment, an apparatus for use in a wellbore includes a valve, a string having a flow conduit and a lower end, and an actuation tool attached to the lower end of the string and adapted to operate the valve if the string is lowered into or raised out of the wellbore.
Other features and embodiments will become apparent from the following description, from the drawings, and from the claims.